Lower extremity weakness is a concern for many persons and often affects the gait of the person. An example of the manifestation of lower extremity weakness is a condition called foot drop where the foot falls forward while walking due to weak or decreased (or lost) motor control of the dorsiflexors muscles. The plantar flexors muscles assist in control the movement of the foot after planting of the heel towards the end of the stride called heal strike. If the plantar flexor muscle group is weak or injured the toes and forward portion of the foot may uncontrollably slaps the ground upon heal strike. Various medical conditions can manifest in the weakening of the dorsiflexor and plantar flexor muscles such as nerve damage from injury, diabetes or motor neuron diseases such as amyotrophic lateral sclerosis (“ALS”), multiple sclerosis, post-polio syndrome, and brain, spinal cord or back injuries.
To compensate for foot drop, the person may exaggerate the swinging motion at the hip of the affected leg, leading with the knee to prevent the toes from dragging or catching on the ground. Some instances of foot drop can be corrected by surgery. However, in those cases in which surgery is ineffective, orthotic devices are typically used to maintain the forward portion of the foot forward or prevent or limit downward motion of the toes as the foot is carried forward during a stride. These orthotic devices, typically called an ankle-foot orthotics, often limit the range of downward motion of the foot at the ankle or completely prevent the downward motion. In use, these orthotics devices often result in an awkward gait. Often these ankle-foot orthotics utilize a stiff plate that the foot rests upon and a support member that travels from the heal of the orthotic to the back of the calf of the leg with a calf strap to hold the orthotic to the leg. The foot plate of these stiff orthotics are often difficult to place in the user's shoes and are uncomfortable.
Another method of preventing the toe portion of the foot from uncontrollably rotating at the ankle is with the use of a top position ankle-foot orthotic that supports the affected foot from the top of the foot and shin. A stiff “L” shaped support member is attached on the top of the foot and above the ankle on the shin. These front-support ankle-foot orthotic devices are often more comfortable than the anterior positioned orthotic, but are difficult to walk in and are best used during less active times when the user does less walking. An more active type front support method uses straps attached at the ball of the foot portion of the user's shoe with stiff straps that cross around the ankle to prevent the toe from dropping downward. Similar designs may use less noticeable, small straps such as cording with an ankle high shoe device such as a high-top athletic shoe. Most of these top of the foot support devices result in a stiff gait because the orthotic limits the rotation at the ankle.
It is desirable to have an ankle-foot orthotic that allows some controlled downward rotation of the foot about the ankle and provide rebound of the foot to allow the user to mimic normal gait without the user exaggerating the throw of the leg from the hip. Likewise, it is desirable to provide an orthotic that is easy to wear and comfortable to increase the use of the orthotic.